ALEPPO PROVINCE, Syria (Reuters) - At a converted warehouse in the midst of a block of residential homes in a northern Syrian town, men are hard at work at giant lathes, shavings of metal gathering around them.

Sacks of potassium nitrate and sugar lie nearby.

In a neat row against the wall is the finished product, homemade mortars. Syrian rebels say they have been forced to make them because their calls for heavy weapons and ammunition to fight President Bashar al-Assad have gone unanswered.

"No one's giving us any support. So we're working on our own to strike Bashar," said a bearded man spinning the metal to create the warhead.

Using the Internet, the workshop of about seven men work together to try and perfect the crude weapons. For explosives, they pick out TNT from unexploded rockets that Assad's forces have fired towards them and repackage them into their own weapons. Each gave different estimates of the mortars' range.

"We're volunteers, we were workers, we were never soldiers. They're locally made. They don't have the strength of the regime's rockets, but they are having good effects," said Abu Mohammed, who said the mortars created a 3-1/2 metre crater.

Another worker said the mortars, which take about a day to make, could reach a distance of 6 km (almost 4 miles).

Although the rebels, who are mostly Sunni Muslim fighters, have made big gains in the northern and eastern parts of Syria in the 21-month conflict, they are outgunned by Assad's forces.

Some rebel groups are receiving supplies from Gulf states, and Western countries say they are giving non-lethal aid. But many rebels say they have not received anything.

Colonel Abdel-Jabbar Oqaidi, who heads the rebels' military council in Aleppo province, told Reuters last week that his forces are fighting without any help from the Western and Arab governments which want Assad removed from power.

"We aren't able to get any weapons from abroad. We have nothing except for the rifle to fight with," said another man at the workshop.

OLD TANKS

The success rate of the weapons is questionable. Two men said the mortars hit 80 to 90 percent of the targets, but there have been problems. Sometimes the mortars do not detonate, other times they explode prematurely.

"The more we practice, the more experience we get," said one of the men, explaining how they discovered that if they let the propelling agent mixture set for too long it absorbed humidity, which in turn stopped the mortar from detonating.

At one of the Aleppo frontline positions, rebels fired the mortars from a homemade tube, fashioned from piping on a mount made from a car axle.

The rebels have also been working on refurbishing weaponry acquired during takeovers of Assad's military bases.

Parked in a residential street, a group of men have been working on fixing a T-72 tank whose gear box was blown.

Abu Jumaa, one of the mechanics working on the 1970s tank, said fighters had taken it from an infantry college in north Syria that had recently fallen to rebel forces.

"We have no tanks, no planes, no artillery. All we have is what we get in spoils and we go to war against him (Assad) with what we get. That's the reality. We're forced to do this," he told Reuters.

"These tanks are useless in the first place. It can't be called a tank, It's a lump of scrap iron," he said gesturing at the chipped army green metal.

Rebel fighters on the frontline consistently complain of shortages of weapons and ammunition that have forced them to stop advances and focus on keeping the ground they have gained.

"We get 3,000 bullets a month. No anti-aircraft missiles ... everything is from the military bases (we take over)," said one young rebel fighter from the Supporters of Mohammed Brigade, wearing a plaid yellow and black turban.

Even though the rebels have managed to seize large quantities of weapons from military bases, they struggle with a chronic shortage of ammunition and weapons to target Assad's fighter jets.

"You see how the planes are striking all of us, not differentiating between old and young ... God has helped us, we've made these rockets and we're using them to hit back at them all over again," said Abu Mohammed.

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